The invention relates to an apparatus for reducing the oversize fraction of chips, especially the overthick fraction, produced during the process of reducing timber products to chips.
From the viewpoint of further processing of the chips, it is important that the size of an individual chip is within a certain range. It is, therefore, necessary to screen the chips and to reduce the size of the chips that have remained oversized during chipping. The oversized fraction of such chips has until now been reduced by using various methods and devices, in which the reduction is carried out by means of a variety of blades or crushers.
However, the reduced chips produced by known solutions do not always fully meet the requirements set for chips because the reduction does not take place in a controlled manner. The blades cut, break or crush oversized chips in random directions, thus reducing the size of some of the chips excessively.
The type of apparatus referred to above is known from the Swedish publication SE 345 820. In this apparatus, the counter blades are arranged essentially in the radial direction. Reducing the size of chips in accordance with this type of solution does not take place in a completely controlled manner either, which means that some of the chips become too small.
A chip reduction apparatus in accordance with the present invention comprises a rotatingly fitted disc-like rotor part to which are attached a number of chipping blades, and a fixed stator part surrounding the top surface of the rotor part, to which stator part are attached a number of counter blades, the blades and counter blades being arranged in a series of chipping chambers, through which the chips to be reduced travel outwardly with respect to the rotational axis of the rotor part. The counter blades are fitted in a position substantially deviating from the radial direction of the rotating shaft, when viewed on the vertical plane with respect to the rotating shaft of the rotor part, and that the chipping chamber is formed by the space between two counter blades, the bottom surface of which space is formed by the top surface of the rotor part, and the roof surface by the bottom surface of the stator part and counter blade opposite to the top If surface of the rotor part, whereby, when viewed in the direction of rotation of the rotor part, the said roof surface is arranged to converge towards the said bottom surface.
Preferably, each chipping chamber has a height defined by the top surface of the rotor part and the bottom surface of the stator part, a length defined by the distance between two counter blades measured in the direction of rotor rotation and an outer perimeter defined by an annular wall or limiter which projects from the stator part toward the rotor part. The bottom surface of the stator part, which defines the upper limit of the chipping chambers, is configured to converge toward the top surface of the rotor part in the direction of rotation of the rotor part. The bottom surface of the stator part reaches its closest approach to the rotor part at the location of each counter blade, the convergence of the bottom surface of the stator, the counter blade and the rotor top surface forming a chipping point. The counter blades are arranged on the fixed stator part in an angular orientation which deviates substantially from radii of the stator part. The counter blades are angled approximately 70xc2x0 from a radial orientation and counter to the direction of rotation of the rotor part. The chipping blades are arranged on the rotor part so the radially outer ends of the chipping and counter blades cross first in the direction of rotation and the chipping process occurs in a radially inward direction along the length of the blades. The angular orientations of the chipping and counter blades also produces an advantageous scissors-like angle between the chipping and counter blades.
In an especially preferred embodiment, the apparatus is operated in an orientation such that the shaft driving the rotor part is essentially vertical and the top surface of the rotor part is essentially horizontal. Chips are introduced into the apparatus through a centrally located chip feed opening. Ejector wings, located at the transition of the chip feed opening and the chipping chambers, guide chips into the chipping chambers and toward the counter blades.
Under ordinary circumstances, centrifugal forces exerted by the rapidly rotating rotor part would force the chips to the perimeter of the rotor part. This tendency is countered in two ways by the present invention. First, the orientation of the counter blades opposes the centrifugal forces and spreads the chips evenly over their length. Second, the chipping action, which proceeds along the chipping and counter blades from their radially outer ends toward their radially inner ends serves to oppose the expected radially outward movement of the chips.
An important feature of the invention is that the chips move in a more controlled manner than before on their surfaces parallel with the longitudinal and lateral direction, on the surface of the disc-like rotor part, especially for the reason that, due to the novel alignment of the counter blades, the chips are pressed against the counter blade continuously, and on the other hand, against the bottom and roof surface of the chipping chamber which converges in a wedge-shaped manner in elevation in the direction of rotation of the rotor part of the chipping chamber, which means that when the chips collide with the counter blade, they always settle in the same manner, leaning on their longitudinally and laterally extending surface against the top surface of the rotor part, and are thus chipped into pieces having a lesser thickness. The mutual alignment of the chipping blade and the counter blade produce a suitable scissor angle which further facilitates the implementation of a controlled chipping process.
An object of the present invention is to produce a new and improved chip reduction apparatus which controls the orientation of chips during the reduction process.
Another object of the present invention is to produce a new and improved chip reduction apparatus which reduces the thickness of chips while retaining the lateral and longitudinal dimensions of the chips.
A further object of the present invention is to produce a new and improved chip reduction apparatus which reduces oversize chips in a controlled manner, maximizing the output of chips having specified dimensions and minimizing the output of excessively reduced chips.
These and other objects, features and advantages of the invention will become readily apparent to those skilled in the art upon reading the description of the preferred embodiments, in conjunction with the accompanying drawings.